What do "best before" dates on food packages mean? Is it safe to eat foods after these dates expire? Are they still nutritious?

"Best before" dates refer to the quality and shelf life of an unopened food product, not safety. They tell you how long a product will retain its optimum flavour, texture and nutritional value when stored under normal conditions. In Canada, best before dates are required on foods that will keep fresh for 90 days or less. However, many foods show best before dates even though they aren't required to do so.

Once you open a food, the best before date is no longer valid. For opened packages, manufacturers are required to provide storage instructions on the label when they differ from normal room temperature – for example, "refrigerate after opening" or "keep refrigerated."

If you store foods properly, many fresh foods like eggs, milk and yogurt can be safely eaten soon after their best before dates have expired. Many packaged foods such as crackers, cookies, canned soup and tinned tuna can be eaten safely long after the best before date. (But be sure to throw away cans that are bulging or leaking – these are not safe to use.)

That doesn't mean these foods will taste as fresh, however. They may have lost some of their flavour and their texture may have changed. Think of best before dates as suggestions about how long food will retain its freshness.

Although canned and packaged foods have a much longer shelf life than fresh foods, keep in mind they can lose anywhere from 5 to 20 per cent of their nutritional content every year. To ensure you use your canned foods while they maintain peak quality and nutrition, label them with the date they were purchased. When you put your groceries away, rotate your stock. Move older cans to the front so they are used first and keep newer ones in the back. Be sure to store canned foods in a cool, dry, dark cupboard.

"Packaged on" dates are different than best before dates. Mandatory for meat and poultry, these dates tell you the day the fresh food was packaged in the store. The "packaged on date" is usually the starting point for how long you can expect the food to stay safe to eat. I don't recommend eating packaged fresh foods once the suggested storage time has lapsed.

Time limits for storage

The following list indicates how long you can store refrigerated foods to retain their highest quality – their freshness, taste and nutrient levels. Time limits for meat, poultry and fish also relate to food safety.

Milk: 7 days after "best before" date, opened or unopened

Yogurt: 7 to 10 days, opened or unopened

Cheese, hard: 3 to 4 weeks opened, 6 months unopened

Butter: 4 weeks after best before date, opened or unopened

Eggs, in shell: 4 weeks

Eggs, hard-cooked: 1 week

Fresh meat: 2 to 4 days

Fresh ground meat: 1 to 2 days

Deli meats: 3 to 4 days

Fresh chicken or turkey, whole or pieces: 2 to 3 days

Fresh ground poultry: 1 to 2 days

Cooked chicken: 3 to 4 days

Fresh fish: 2 to 3 days

Fresh shellfish: 12 to 24 hours

Leftover soups, stews, casseroles: 3 to 4 days

Jams and jellies: 3 to 4 months, opened

Mayonnaise: 2 to 3 months, opened

Mustard: 1 year, opened

Ketchup: 6 months, opened

Salad dressing or vinaigrette, bottled: 6 to 9 months, opened

Salsa, bottled: 4 weeks, opened

Leslie Beck, a registered dietitian, is the national director of nutrition at BodyScience Medical. www.lesliebeck.com